Will there be a common platform
The big problem about ARM right now is that virtually every computer requires its own OS image. While on PCs you can boot your OS on virtually all PCs with just 2 images, ARM systems are incredibly diverse.
Seriously on a PC you can blindly access some ports and you will always find a serial port. Same goes for basic graphics, USB, SATA or whatever you could wish for. And for things that do not have fixed ports you can query the devices in a standardized way.
This needs to be established first before we can think about having ARM servers. There's no point in having one that can only run version X of operating system Y.
Hopefully eventually such a standard platform will move into the mobile world. This would finally mean that you could choose your operating system independently of your manufacturer. You could even update your software without it. Suddenly a mobile device might actually be useful for a longer period of time.